This invention is concerned with the separation of discrete minerals which are bonded together mechanically rather than on a molecular basis. The invention is particularly but not necessarily exclusively concerned with the separation of pyrites, ash and other impurities from coal in the production of a fuel comprising coal particles, oil and water. A fuel of the kind with which the invention is concerned is described in my U.S. Pat. No. 3,941,552 issued Mar. 2, 1976. In that patent the problems of contamination of the coal is discussed and it is proposed that there be incorporated into the fuel a quantity of lime to reduce objectionable emissions when the fuel is burned. The present invention is specifically directed to the removal, prior to combustion, of impurities contaminating the coal such as, for example, pyrites and ash forming constituents. The present invention additionally is concerned with the diminution of particle size prior to the incorporation of the particles into the fuel.